(1) Field of the Invention
The present invention relates to a method for preliminarily printing a blank for a tapered draw-formed body.
(2) Description of the Related Art
Draw-forming of a surface-treated steel sheet such as a tinplate or tin-free steel sheet or a metal sheet such as an aluminium sheet is widely adopted for the manufacture of a so-called seamless can (two-piece can) and a metal cap. Coating or printing of individual formed bodies after the forming operation requires a complicated operation, and therefore, coating or printing of a flat blank before the draw-forming is desirable.
In Japanese Examined Patent Publication No. 63-61658, we proposed a method for making a draw-formed body having a printed image on the side wall portion by draw-forming a preliminarily printed blank, wherein an image on an original to be printed is subjected to photoelectric scanning to convert the original image to a picture element signal on rectangular coordinates, the rectangular coordinates are transformed to an annular plane having an area almost equal to the area of the rectangle of the coordinates while increasing the number of picture elements in the circumferential direction and decreasing the number of picture elements in the radial direction, and when the number of picture elements is increased, new coordinates of the picture element present in a space between the transformed coordinates corresponding to adjacent picture elements of the rectangular coordinates are calculated, picture element signals on the transformed coordinates are read and inputted in a printing plate and the obtained printing plate is used for printing the blank.
According to this prior art technique, an image of a rectangular image can be reproduced finely and precisely by units of dots or picture elements on an annularly developed plane of a printing plate, and a printed image corresponding precisely to the image of the rectangular original can be advantageously formed on the circumferential side wall portion of the draw-formed body by using this printing plate. However, in the case where the draw-formed body is a tapered draw-formed body such as a vessel for filling jelly or soft adzuki-bean jelly, the reproduced image is flattened in the lateral direction at an upper part, and the method is still insufficient in the faithful reproduction of the original image.
Namely, in the side face portion of a draw-formed vessel having a tapered side wall, if the image is radially expanded from the lower part to the upper part at an angle corresponding to the tapering angle, comfortable vision and appearance are given to human eyes. However, according to the above-mentioned prior art technique, the degree of the upward expansion from the lower part exceeds the optimum range, a picture, photograph or letter pattern indicating the content is flattened in the lateral direction and the appearance and commercial value is degraded.